Transcript Design Consideration for Process Safety

Hazard Survey
• Dow Fire and Explosion Index is the most popular
form of hazard survey.
• A formal systematized approach using a ranking
form (similar to an income tax form).
• The final rating number provides a relative
ranking of the hazards.
• The approach also contains a mechanism for
estimating the dollar loss in the event of an
accident.
F&EI Form
1. Penalty column. Penalties for various unsafe
situations are placed in this column.
2. The second column contains the penalty actually
used. This allows for a reduction or increase in
the penalty based on extenuating circumstances
not covered in the form. In case of uncertainty,
the value in the first column is used.
3. The final column is used for computation.
Procedure
1. Conceptually divide the process into
separate units. A process unit is a pump, a
reactor or a storage tank, etc. Select the
units that experience shows to have the
highest likelihood of hazard.
2. Determine the material factor (MF).
Procedures are available for mixtures and
materials not listed in Table.
Procedure
3.
Determine the general process hazards. Penalties are
applied for
- Exothermic reactions that might self-heat.
- Endothermic reactions that could react due to an
external heat source such as a fire.
- Material handling and transfer, including pumping and
connection of transfer lines.
- Enclosed process units preventing dispersion of
escaped vapors.
- Limited access for emergency equipment.
- Poor drainage of flammable materials away from the
process unit.
Procedure
4. Penalties for special process hazards
- Toxic materials.
- Less than atmospheric pressure operation with a
risk of outside air entering.
- Operation in or near the flammable limits.
- Dust explosion risk.
- Higher than atmospheric pressure.
- Low temperature operation with potential
embrittlement of carbon steel vessels.
Procedure
4. Penalties for special process hazards
- Quantity of flammable material.
- Corrosion and erosion of process unit structure.
- Leakage around joints and packings.
- Use of fired heaters, providing a ready ignition
source.
- Hot oil heat exchange systems where the hot oil
is above its ignition temperature.
- Large rotating equipment, including pumps and
compressors.
Computation of F&EI
•
•
•
•
The general process hazard factor: F1
The special process hazard factor: F2
The unit hazard factor: F3=F1×F2
F&EI=MF×F3
Degree of Hazard
F&EI
Degree
1-60
Light
61-96
Moderate
97-127
Intermediate
128-158
Heavy
159-up
Severe
Consequence Analysis
• MPPD: the maximum probable property
damage.
• MPDO: the maximum probable days outage.
• Worksheet in Figure 10-4
Risk Analysis Summary
• F&EI (A-1) + correlation →
• damage radius (A-2) →
• Dollar value of the equipment with damage radius
(A-3)
• Correlation → Damage factor (B)
• A-3 × B = base MPPD (C)
• Credit factor: D = C1 × C2 × C3
• C × D = actual MPPD (E) →
• Correlation + E → MPDO (F)
Example
A gasoline filling station contains a 10000 gallon
tank with 4 gas pumps. The tank is stored
underground and vented to the air. Proper vents
with flame arrestors are provided. The tank is
made of steel. Some deterioration by corrosion.
The station has both fixed CO2 fire extinguisher and
portable equipment. A remote shutdown control is
installed in the station house.
Solution
• MF=16 (Table 10-1)
• General process hazards: Item C Penalty =
0.5. Thus, F1=1.0+0.5=1.5
• Special process hazards: Item A penalty =
0.2, Item C1 penalty = 0.5, Item C3 penalty
= 0.8, Item G:
3
3
(
10000
gal)(1
ft
/
7
.
48
gal)(62.4
lb
/
ft
)(0.7)  58400 lb m
•
m
(58400 lbm)(18800BTU/lbm)  1.10  109 BTU
Solution
• Figure 4 + Correlation B →G2 penalty =
0.4
• Item H penalty = 0.1
• F2 = 3.0
• F3 = 1.5 × 3.0 = 4.5
• F&EI = 4.5 × 16 = 72.0
• Moderate!